Electrical inductive apparatus with clamping and air-gap adjusting frame



Apnl 1, 1969 c. E. DERBYSHIRE ET AL 3,436,707

ELECTRICAL INDUCTIVE APPARATUS WITH CLAMPING AND AIR-GAP ADJUSTING FRAME Filed on. so, 1967 mum Iii

II n fitter-274g United States Patent US. Cl. 336-134 6 Claims ABSTRACT OF THE DISCLOSURE A dry type transformer with a clamping and air-gap adjusting frame. This frame includes front and rear clamping straps that extend in parallel relationship on each side of a leg of a magnetic core, the clamping straps having extensions that project upwardly above the upper yoke of the magnetic core. Crosshead members join the opposed extensions of the front and rear clamping straps to form a screw-press superstructure. Platens of the superstructure are disposed along the edges of the laminations of the upper yoke of the magnetic core with the heads of press bolts engaging the platens in screw-press relationship to selectively position the upper yoke with respect to one or more of the legs of the magnetic core thereby to permit adjustments to be made to the air gap of the magnetic core during assembly. During operation, the screw-press superstructure of the clamping and air-gap adjusting frame restrains edgewise movement of the laminations of the upper yoke to minimize noise during operation.

Background of the invention This invention relates generally to inductive apparatus such as transformers, and more particularly to inductive apparatus with an improved clamping and air-gap adjusting frame.

In conventional constructions of stationary inductive apparatus, as for example dry type transformers, the magnetic core is formed of stacked laminations of magnetic material held in assembled relation by frame members which are disposed along the magnetic core and provide support for the apparatus. In many applications, such as computers, communication equipment, lighting and others, it is desirable to minimize the effects of magnetostrictive deformations which take place in the laminations of the magnetic core of the transformer when the unit is energized from an alternating current power source.

It is well known that laminations of a magnetic core when magnetized during operation undergo minute changes in size and shape, which often cause perceptible movements in the laminations. Audible humming results from these vibrations, and frequently the air-gap spacing may be affected thereby changing the inductance of the coil and core assembly. In applications of transformers used in static converters, it is particularly important that the inductance of the transformer be controlled and maintained within close tolerances.

In butt-stacked magnetic cores, one or more air gaps in the path of the magnetic flux are provided between a yoke which is in an abutting relationship with the legs of the E-shaped core section. In addition to other factors, the inductance of such magnetic core and coil assemblies depends upon the air gap in the magnetic flux path. Usually the final adjustment of inductance for a particular transformer design is made by varying the air gap to obtain the desired value of inductance. In the past exice ternal jigs and the like, not a part of the transformer, have been used to adjust and set the air gap. It would be desirable, of course, to provide an inductive apparatus wherein the air gap can be adjusted and set without the use of jigs and the like and wherein the air gap can be securely maintained over the life of the apparatus thereby to insure that the inductance of the transformer will remain substantially constant without producing objectionable noise.

Accordingly, it is a general object of the invention to provide an improved electrical inductive apparatus.

A more specific object of the invention is to provide an inductive apparatus with an improved clamping and adjusting frame superstructure arrangement.

It is another object of the invention to provide an inductive apparatus wherein the effects of magnetostriction on audible noise generation are effectively minimized.

A further object of the invention is to provide an improved inductive apparatus wherein the air gap of the magnetic core can be readily adjusted during assembly and wherein the air-gap spacing can be maintained during field operation of the apparatus.

Summary of the invention In accordance with one form of our invention we have provided an electrical inductive apparatus having an improved clam-ping and air-gap adjusting superstructure frame arrangement. The electrical inductive apparatus includes a magnetic core formed of laminations of magnetic material and having a plurality of legs and an upper and lower yoke connecting the legs to define a magnetic flux path. At least one electrical coil assembly is disposed on one of the legs, and at least one of the legs is spaced from a yoke to provide an air gap in the magnetic flux path.

The clamping and air-gap adjusting frame includes front and rear clamping straps extending in parallel relationship on each side of a leg of the magnetic core. The clamping straps have extensions that project upwardly above the upper yoke of the magnetic core in opposed relation. To compressively hold the front and rear clamping straps against the magnetic core for clamping the laminations thereof, suitable means such as through bolts and horizontal frame members are disposed along the front and rear clamping straps.

According to an important aspect of our invention, platens are positioned along the edges of the laminations of the upper yoke of the core, and crosshead members join pairs of the opposed extensions projecting from the front and rear clamping straps. A plurality of press bolts are threaded into the crosshead members for engaging the platens in screw-press relationship to permit the upper yoke to be selectively positioned and to allow precise adjustments to be made in the air gap of the magnetic core during assembly. Also, the platens restrain edgewise movement of the laminations of the upper yoke during operation of the electrical apparatus.

An important advantage resulting from our improved clamping and air-gap adjusting frame superstructure arrangement is that an air gap selected to provide a predetermined value of inductance can be maintained in service, and noise resulting from magnetostrictive effects during operation are effectively minimized. With the improved air-gap adjusting superstructure of the frame, precise adjustments of the air gap of a magnetic core during assembly are readily made.

The subject matter of our invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, both as to organization and advantages may be best understood by referring to the following description taken in conjunction with the accompanying drawing in which:

Brief description of the drawing FIGURE 1 is a perspective view of an inductive apparatus embodying one form of our invention;

FIGURE 2 is a partially exploded perspective view of the clamping and air-gap adjusting frame of the inductive apparatus shown in FIGURE 1, only one set of press screws, one platen and crosshead being illustrated; and

FIGURE 3 is a plan view of the E and I lamination stack of the magnetic core of the inductive apparatus as shown in FIGURES 1 and 2 and illustrating the air-gap spacing employed.

Description of the preferred embodiment Referring now more specifically to the figures of the drawing, we have shown therein a dry type transformer embodying one form of our invention. The transformer 10 includes a magnetic core 11, a clamping and air-gap adjusting frame 12 with a screw-press superstructure 13, and coil assemblies 14, 15 and 16. Although our invention has been exemplified in a dry type transformer, it will be appreciated that the improved clamping and air-gap adjusting arrangement can be used in liquid dielectric filled transformers and other types of reactors having air gaps in the magnetic flux path.

The magnetic core 11 of transformer 10 has three legs 17, 18 and 19 (see FIGURE 3) which are mechanically and magnetically connected through air gaps 20, 21, 22 with an upper yoke 23 and a lower yoke 24. The E- and I-shaped core sections of the magnetic core 11 are generally made up of stacks of relatively thin laminations of magnetic material. The core legs 17, 18 and 19 have mounted thereon the coil assemblies 14, 15 and 16 respectively, core assemblies 14, 16 containing the primary winding, and the coil assembly 15 containing the secondary winding of the transformer 10.

As is best seen in FIGURE 2, the coil assemblies 14, 15 and 16 are secured to the core legs by wedges 251, 26 and 27, which are inserted between the underside of the coil assemblies 14, 15 and 16 and the core legs. The coil assemblies 14, 15 and 16 are of conventional construction. The turns of the coil assemblies 14, 15 and 16 are wound on spools (not shown) and insulating wrappers 28, 29 and 30 are provided on the outside of the coils? to provide and insulate the coil windings. It will be understood that leads 31, 32 are brought out from the coils for connection in an external electrical circuit. Since the manner in which these leads are connected to the coil winding forms no part of the present invention, the specific connections of these leads and the windings of the coil assemblies 14, 15 and 16 have been omitted in interest of brevity and clarification.

In order to securely clamp the laminations of the magnetic core 11 together, front and rear clamping straps 33, 34, 35, 36, 37 and 38 are placed along the outer face of the core legs 17, 18 and 19 of the magnetic core 11 and are compressively engaged against the faces by the angles 39, 40, 41 and 42 and through bolts 43, 44, 45, 46, 47 and 48 with their associated nuts 49, 50 and 51. It will be noted that the clamping straps 33, 34, 35, 36, 37 and 38, as is best seen in FIGURE 2, have extensions 52, 53, 54, 55, '56 and 57 respectively that project vertically beyond the yoke 23 of magnetic core 11. As will hereinafter be more fully explained, these extensions mount the airgap adjusting and clamping superstructure 13 of the frame It will be seen that the through bolts 43, 44 and 45 extend through suitable holes in the magnetic core 11, which are aligned with holes 58, 59 and 60 in the bottom horizontal clamping angle 40. Similar aligned holes are provided in the rear horizontal clamping angle 41. A functionally similar arrangement is used to firmly hold the upper portion of the magnetic core together. It will be seen, however, that front clamping straps 33, 34 and 35 have elongated vertically extending slots 61, 62 and 63 formed therein to permit vertical adjustment to be made in the position of the yoke 23 with respect to the ends of the core legs and thereby vary the air gaps. It will be appreciated that identical slots are provided in the rear vertical straps 36, 37 and 38, which are not shown in FIG- URE 2. Since the clamping straps 33, 34, 35, 36, 37 and 38 bridge the air gaps of the magnetic 'core 11, it will be understood that the clamping straps are preferably made of nonmagnetic material. In the illustrated embodiment of our invention, the vertical clamping straps were fabricated of stainless steel.

Referring now more particularly to FIGURES l and 2 and screw-press assembly 65 shown in the exploded View, we will now more fully describe the screw-press superstructure. It will be noted in the exploded View of FIG- URE 2 we have only illustrated the parts of one screwpress assembly 65 since the screw-press assemblies 66 and 67 are of the same construction.

In the illustrated embodiment of our invention, a channel-shaped member was used to form the crosshead member 68 of screw-press assembly 65. The channel-shaped crosshead member 68 was bolted to the front and rear extensions 52, 55 of the vertical clamping straps 33, 36. It will be appreciated that this crosshead member 68 may be fabricated as an integral part of the vertical clamping straps 33, 36 or may be attached thereto by other suitable means such as Welding. As is best seen in FIGURE 1, the heads of three press bolts 69, 70 and 71 engage a platen 72 that is positioned against the edges of the laminations of the yoke 23. Although in the illustrated embodiment of our invention the platen 72 was a flat plate, it will be appreciated that it may be desirable in some designs to use an angle, channel or other reinforced structural member as the platen 72. It will be appreciated that this crosshead member 68 may 69, 70 and 71 were used in the illustrated embodiment of our invention, any number of press bolts may be used depending upon the stack height of the magnetic core 11. The press bolts 69, 70 and 71 are threaded into taps 73, 74 and 75 in crosshead member 68. Adjustments to the air gaps are made by turning the bolt heads until the desired air gap is obtained. The nuts 76 are provided to securely lock the bolts 69, 70 and 71 and thereby prevent the bolts from coming loose during operation of the transformer 10.

In the assembly of an inductive apparatus according to our invention, the vertical mounting straps 33, 34, 35, 36, 37 and 38 are initially assembled against the legs of the magnetic core 11. The lower through bolts 43, 44 and 45 are then placed through the aligned openings in the vertical straps, the laminations of the core 11 and the lower horizontal clamping angles 40 and 41. The bolts 43, 44 and 45 are then tightened to draw the lower horizontal clamping angles tightly against the laminations of the core 11. If desired, before clamping a resin adhesive may be applied to the laminations for the purpose of bonding the core structure. The coil assemblies 14, 15 and 16 are then mounted on the legs, and the wedges 25, 26 and 27 are inserted between the clamping straps 33, 34 and 35 and the underside of the coil assemblies 14, 15 and 16. If desired, gap spacers may be placed on the ends of the legs.

At this stage of the assembly process, the I-shaped core section may now be positioned on the gap spacers between the vertical clamping straps 33, 34, 35, 36, 37 and 38. The through bolts 46, 47 and 48 are then inserted through the slots in the vertical clamping straps and through the holes in laminations of the I-shaped core section. With the through bolts 46, 47 and 48 in place, the upper horizontal clamping angles 39 and 42 are now assembled on the ends of the bolts, and the nuts 49, 50 are tightened to draw the clamping angles against the vertical straps sufliciently to hold but not rigidly constrain the laminations of the yoke 23. It will be understood that the yoke 23 should be positioned so that an air-gap spacing greater than the desired gap spacing is initially obtained.

The next step in the process of the assembly is to place the platens 72 in position and assemble the crosshead members 68 and press bolts 69, 70 and 71. With all of the crosshead members and press bolts assembled, the windings of the coil assemblies 14, 15 and 16 may now be connected to a conventional indutcance measuring circuit, and the air gaps 20, 21 and 22 are adjusted by turning the bolt heads of the press bolts with a wrench progressively until the desired inductance reading is obtained. The lock nuts 49 and 50 of the upper horizontal clamping angles 42 and 39 may now be securely tightened to complete the assembly of the transformer 10. At this time, if desired, additional resin adhesive may be applied and the assembly may be subjected to an impregnation and during treatment. If required, the transformer may be encapsulated in a resin encapsulant, potted in a case, or otherwise encased.

By way of a more specific exemplification of the invention, in the transformer shown in FIGURES 1 and 2 the primary winding (coil assemblies 14 and 16) included 74 turns of rectangular aluminum wire having a cross-section of 0.485 by 0.175 of an inch, and the secondary windings (coil assembly had 34 turns of rectangular aluminum wire with a cross-section of 0.290 by 0.155 of an inch. The transformer 10 was adapted for connection to either a 115 or a 230 volt power supply to provide an output voltage of 92.6 or 185.2 volts, respectively. Noise tests were carried out on comparable transformers with and without the improved screw-press superstructure. For the transformer without the screwpress superstructure, the decibel readings after heat runs ranged between 110 and 130. For the transformer with the screwpress superstructure, the decibel readings after heat runs were less than 60 indicating a significantly reduced noise level.

From the foregoing description, it will be apparent that we have provided a stationary inductance apparatus having an improved screw-press clamping arrangement for restraining movement of the laminations of an I-shaped core section and for permitting the air gap to be precisely adjusted. With the improved superstructure arrangement, it was possible to appreciably reduce the noise level of a. transformer without sacrificing the electrical operating characteristics.

While we have illustrated our invention in connection with a magnetic core fabricated of stacks of E and I laminations, it will be understood that the invention may be used with laminated core structures having different lamination configurations, such as for example an I-shaped and a U-shaped configuration and other It will be apparent to those skilled in the art that various changes and modifications ma be made to the particular embodiment of the invention which we have described herein without departing from the principle of the invention. For example, many modifications may be made to the structural arrangement of the frame members and to the superstructure. It is to be understood, therefore, that we intend by the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical inductive apparatus comprising a magnetic core formed of laminations of magnetic material and having a plurality of legs and an upper and lower yoke connecting said legs to define a magnetic flux path; at least one electrical coil assembly disposed on one of said legs, at least one of said legs being spaced from a yoke to provide at least one air gap in the magnetic flux path; and a clamping and air-gap adjusting frame for holding the laminations of the magnetic core in assembled relation and for adjusting the spacing of the air gap to provide a predetermined magnitude of inductance during operation, said clamping and air-gap adjusting frame including front and rear clamping straps extending in parallel relationship on each side of a leg of said magnetic core, said clamping straps having extensions projecting upwardly above said upper yoke in opposed relation, means for compressively holding said front and rear clamping straps against said magnetic core for clamping the laminations thereof, crosshead members joining pairs of the opposed extensions, platens disposed along the edges of the laminations of the upper yoke, and a plurality of press bolts threaded into said cross members for engaging said platens in screw-press relationship to selectively position said upper yoke with respect to the one or more of said legs thereby to permit adjustment to be made to said air gap during assembly and to restrain edgewise movement of laminations of the upper yoke during operation of said electrical inductive apparatus.

2. The electrical inductive apparatus of claim 1 wherein said clamping straps are of nonmagnetic material.

3. In a stationary inductive apparatus, a magnetic core formed of laminations of magnetic material and including a plurality of vertically extending legs and upper and lower yokes connecting said legs to provide a magnetic flux path; electrical coil assemblies disposed on said legs, at least one of said legs being spaced from one of said yokes to provide an air gap in the path of magnetic flux; a clamping and air-gap adjusting frame, said clamping and air-gap adjusting frame including vertical clamping straps disposed on opposite sides of each leg for clamping together the laminations thereof, means fixedly securing said clamping straps to compressively engage the laminations of the lower yoke, said front and rear straps having front and rear extensions respectively projecting vertically beyond said upper yoke, crosshead members bridging said front and rear extensions, platens disposed horizontally on the upper edges of the laminations of the upper yoke between said front and rear extensions, a plurality of press bolts threadingly engaged in said crosshead members and in screw-press relationship with said platen, and means for compressively supporting said upper yoke in a fixed vertically adjustable relationship with respect to said front and rear straps thereb to permit the air gap to be adjusted during assembly of said electrical inductive apparatus by selectively rotating said press bolts, and said platens of said clamping and air-gap adjusting frame restraining edgewise movement of the laminations of the upper yoke during operation of said electrical inductive apparatus.

4. In the stationary inductive apparatus of claim 3 wherein said clamping straps are of nonmagnetic material.

5. An electrical inductive apparatus comprising a magnetic core formed of laminations of magnetic material and having a plurality of vertical legs connected by upper and lower yokes to define a magnetic flux path; at least one electrical coil assembly mounted on one of said legs, said legs being spaced from one of said yokes to provide at least one air gap in the magnetic flux path; and a clamping and air-gap adjusting frame including a plurality of front and rear vertical clamping straps, each of said vertical clamping straps having an extension projecting upwardly above the upper yoke, a plurality of crosshead members joining said front and rear clamping straps, a plurality of platens disposed along the edges of the laminations of the upper yoke, a plurality of press bolts threaded into said crosshead members for engaging said platens in screw-press relationship, means on said front and rear straps for affording relative vertical movement of the upper yoke with respect to the ends of the legs of the magnetic core when the press bolts are turned to force a platen compressively against the upper yoke,- and means for fixedly holding said front and rear vertical clamping straps compressively against the upper yoke References Cited to maintain an air gap that provides a predetermined UNITED STATES PATENTS magnitude of inductance during operation of said electri 2,157,324 5/1939 Crout *1 4 cal inductive apparatus, said platens during operation re- 3,171,018 2/1965 Lawler 336134 XR straining edgewise movement of the laminations of the 5 3,267,400 8/1966 Cfaige 336134 upper yoke. DARRELL L. CLAY, Primary Examiner.

6. The electrical inductive apparatus set forth in claim T. J. KOZMA, Assistant Examiner. 5 wherein said vertical clamping straps are of nonmag- CL netic material. 10 336--210 

